1. Field of the Invention
This invention relates to apparatus for treating portions of articles, and more particularly, to apparatus for spot electroplating layers of metals on conductive articles.
This invention is suited for use in the manufacture of semiconductive devices such as transistors, diodes, integrated circuits and the like. It is particularly suited for electroplating gold layers on portions of nickel or copper lead frames that may be used for semiconductor devices, such as integrated circuit chips which may be bonded to gold-patterned ceramic substrates. However, this invention is also equally well suited for other treating applications, such as those involving electrochemical action, anodizing, polishing, cleaning or the like, wherein the treatment of a small portion of an article is desired.
2. Description of the Prior Art
In the manufacture of integrated circuits, leads of each of a plurality of integrated circuit chips are bonded individually to gold conductive patterns formed on insulating ceramic substrates. In order to connect these patterns to other circuits, leads are connected to these patterns and are often formed from a lead frame stamped from a sheet of conductive metal such as nickel, copper or the like. The lead frame has a separate group of leads for each conductive pattern of each substrate, and these leads are bonded to the substrate. Each group has the outer ends of each lead interconnected to carrier strips and their opposed inner free ends bonded to the conductive pattern of each substrate. The leads are also interconnected intermediate their ends by relatively narrow support strips. The carrier strips have outer portions perforated for feeding them through various treating operations. Both the carrier and support strips are severed to separate the individual leads prior to the completion of the ultimate integrated circuits.
In the prior art techniques, a layer of gold has often been formed over the entire lead frame by electroless or electroplating. The purpose of such gold layer is to improve any bonds made to the lead frame. In other prior art techniques, a nonuniform layer of gold has been formed over the entire lead frame with the greatest thickness being concentrated at those portions of the frame where the bonding of an integrated circuit chip or other semiconductive device is to take place. (See Rackus et al. U.S. Pat. No. 3,692,638.) Since the carrier and support strips are ultimately trimmed away it is desirable to have no gold on them. Since the substrates are bonded to the inner free ends of the leads, it is desirable to have a gold layer thereon to improve bondability. Since no substrates are bonded to the remainder of the leads, a gold layer thereon is not necessary. The absence of gold on these strips eliminates expensive and time-consuming reclamation processes to recover the gold from these strips. The absence of gold everywhere except where substrate bonding is to take place can result in a very desirable efficient use and substantial savings of gold.
In treating the lead frames by plating or similar techniques, it is also desirable to carry out such treatment while the frames are advancing in a continuous motion. This can result in treating at great speeds and increase the output of the treating facilities.
Finally, it is also desirable to bring about selective or spot treatment, including plating, without the use of any masks. The elimination of masks often simplifies the treating processes and eliminates any mask replacement or cleaning steps.